About 99% of the body's calcium is stored in the bones, but cells (particularly muscle cells) and blood also contain calcium. Calcium is essential for the following:
The body precisely controls the amount of calcium in cells and blood. The body moves calcium out of bones into blood as needed to maintain a steady level of calcium in the blood. If people do not consume enough calcium, too much calcium is mobilized from the bones, weakening them. Osteoporosis can result. To maintain a normal level of calcium in blood without weakening the bones, people need to consume at least 1,000 to 1,500 milligrams of calcium a day. The level of calcium in blood is regulated primarily by two hormones: parathyroid hormone and calcitonin.
Parathyroid hormone is produced by the four parathyroid glands, located around the thyroid gland in the neck. When the calcium level in blood decreases, the parathyroid glands produce more parathyroid hormone. When the calcium level in blood increases, the parathyroid glands produce less hormone. Parathyroid hormone does the following:
Calcitonin is produced by cells of the thyroid gland. It lowers the calcium level in blood by slowing the breakdown of bone, but only slightly.
In hypocalcemia, the calcium level in blood is too low.
About 40% of the calcium in blood is attached (bound) to proteins in blood, mainly albumin. Protein-bound calcium acts as a reserve but has no active function in the body. Only unbound calcium affects the body's functions. Thus, hypocalcemia causes problems only when the level of unbound calcium is low. Unbound calcium has an electrical (ionic) charge, so it is called ionized calcium.
Hypocalcemia most commonly results when too much calcium is lost in urine or when not enough calcium is moved from bones into the blood. Causes of hypocalcemia include the following:
The calcium level in blood can be moderately low without causing any symptoms. Over time, hypocalcemia can affect the brain and cause neurologic or psychologic symptoms, such as confusion, memory loss, delirium, depression, and hallucinations. These symptoms disappear if the calcium level is restored.
An extremely low calcium level may cause tingling (often in the lips, tongue, fingers, and feet), muscle aches, spasms of the muscles in the throat (leading to difficulty breathing), stiffening and spasms of muscles (tetany), seizures, and abnormal heart rhythms.
Hypocalcemia is often detected by routine blood tests before symptoms become obvious. Doctors measure the total calcium level (which includes calcium bound to albumin) and the albumin level in blood to determine whether the level of unbound calcium is low.
Blood tests are done to evaluate kidney function and to measure magnesium, phosphate, parathyroid hormone, and vitamin D levels. Other substances in blood may be measured to help determine the cause.
Calcium supplements, given by mouth, are often all that is needed to treat hypocalcemia. If a cause is identified, treating the disorder causing hypocalcemia or changing drugs may restore the calcium level.
Once symptoms appear, calcium is usually given intravenously. Taking vitamin D supplements helps increase the absorption of calcium from the digestive tract. Thiazide diuretics may be given to decrease the excretion of calcium by the kidneys, particularly when hypocalcemia is caused by hypoparathyroidism.
In hypercalcemia, the level of calcium in blood is too high.
Causes include the following:
Symptoms and Diagnosis
Hypercalcemia often causes no symptoms. The earliest symptoms are usually constipation, nausea, vomiting, abdominal pain, and loss of appetite. People may excrete abnormally large amounts of urine, resulting in dehydration and increased thirst.
Very severe hypercalcemia often causes brain dysfunction with confusion, emotional disturbances, delirium, hallucinations, and coma. Muscle weakness may occur, and abnormal heart rhythms and death can follow. Long-term or severe hypercalcemia commonly results in kidney stones containing calcium. Less commonly, kidney failure develops, but it usually resolves with treatment. However, if enough calcium accumulates within the kidneys, damage is irreversible.
Hypercalcemia is usually detected during routine blood tests.
If hypercalcemia is not severe, correcting the cause is often sufficient. If people have mild hypercalcemia or conditions that can cause hypercalcemia and if their kidney function is normal, they are usually advised to drink plenty of fluids. Fluids stimulate the kidneys to excrete calcium and help prevent dehydration.
If the calcium level is very high or if symptoms of brain dysfunction or muscle weakness appear, fluids and diuretics are given intravenously as long as kidney function is normal. Dialysis is a highly effective, safe, reliable treatment, but it is usually used only for people with severe hypercalcemia that cannot be treated by other methods.
Several other drugs (including bisphosphonates, calcitonin, corticosteroids, and, rarely, plicamycin) can be used to treat hypercalcemia. These drugs work primarily by slowing the release of calcium from bone.
Hypercalcemia caused by cancer is particularly difficult to treat. If the cancer cannot be controlled, hypercalcemia usually returns despite the best treatment.
Last full review/revision August 2008 by Larry E. Johnson, MD, PhD